<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8" />
		<title>Document</title>
		<style>
			*{
				margin: 0;
				padding: 0;
			}
			html,body{
				font-size: 50px;
			}
			#demo1{
				width: 400px;
				height: 400px;
				background-color: orange;
				font-size: 20px;
			}
			#demo2{
				width: 4rem;
				height: 4rem;
				background-color: gray;
			}
		</style>
	</head>
	<body>
		<div id="demo1">
			<div id="demo2">
			</div>
		</div>
	</body>
</html>